The application of diagnostic ultrasound in pediatrics has become widely accepted and is being utilized more frequently in the diagnosis and management of patients. Since the technique is accurate, painless and without known risk, it has great appeal as a noninvasive diagnostic method. When a method is extensively used, it is essential to know about its safety. The purpose of this discussion is to provide some understanding of the interaction of ultrasound and biologic tissue and the possible potential hazards of the technique. Diagnostic ultrasound as applied in medicine may be utilized in three ways-as continuous Doppler, pulsed-sonar or Doppler-sonar.